Apache Tomcat Development

CGI How To

Table of Contents

Introduction

The CGI (Common Gateway Interface) defines a way for a web server to
interact with external content-generating programs, which are often
referred to as CGI programs or CGI scripts.

Within Tomcat, CGI support can be added when you are using Tomcat as your
HTTP server and require CGI support. Typically this is done
during development when you don't want to run a web server like
Apache httpd.
Tomcat's CGI support is largely compatible with Apache httpd's,
but there are some limitations (e.g., only one cgi-bin directory).

CGI support is implemented using the servlet class
org.apache.catalina.servlets.CGIServlet. Traditionally,
this servlet is mapped to the URL pattern "/cgi-bin/*".

By default CGI support is disabled in Tomcat.

Installation

CAUTION - CGI scripts are used to execute programs
external to the Tomcat JVM. If you are using the Java SecurityManager this
will bypass your security policy configuration in catalina.policy.

To enable CGI support:

There are commented-out sample servlet and servlet-mapping elements for
CGI servlet in the default $CATALINA_BASE/conf/web.xml file.
To enable CGI support in your web application, copy that servlet and
servlet-mapping declarations into WEB-INF/web.xml file of your
web application.

Uncommenting the servlet and servlet-mapping in
$CATALINA_BASE/conf/web.xml file enables CGI for all installed
web applications at once.

Set privileged="true" on the Context element for your
web application.

Only Contexts which are marked as privileged are allowed to use the
CGI servlet. Note that modifying the global $CATALINA_BASE/conf/context.xml
file affects all web applications. See
Context documentation for details.

Configuration

There are several servlet init parameters which can be used to
configure the behaviour of the CGI servlet.

cgiPathPrefix - The CGI search path will start at
the web application root directory + File.separator + this prefix.
By default there is no value, which results in the web application root
directory being used as the search path. The recommended value is
WEB-INF/cgi

executable - The name of the executable to be used to
run the script. You may explicitly set this parameter to be an empty string
if your script is itself executable (e.g. an exe file). Default is
perl.

executable-arg-1, executable-arg-2,
and so on - additional arguments for the executable. These precede the
CGI script name. By default there are no additional arguments.

envHttpHeaders - A regular expression used to select the
HTTP headers passed to the CGI process as environment variables. Note that
headers are converted to upper case before matching and that the entire header
name must match the pattern. Default is
ACCEPT[-0-9A-Z]*|CACHE-CONTROL|COOKIE|HOST|IF-[-0-9A-Z]*|REFERER|USER-AGENT

parameterEncoding - Name of the parameter encoding
to be used with the CGI servlet. Default is
System.getProperty("file.encoding","UTF-8"). That is the system
default encoding, or UTF-8 if that system property is not available.

passShellEnvironment - Should the shell environment
variables from Tomcat process (if any) be passed to the CGI script? Default is
false.

stderrTimeout - The time (in milliseconds) to wait for
the reading of stderr to complete before terminating the CGI process. Default
is 2000.

The name and path of the CGI script to search for in the CGI search path
depends on how the Servlet has been mapped. If the pathInfo is
null, the servletPath will be used. If the
pathInfo is not null then the
servletPath is appended to the CGI search path and the
pathInfo is used.

The search will start with the first path segment and expand one path segment
at a time until no path segments are left (resulting in a 404) or a matching
script is found in the CGI search path. Any remaining path segments will be
passed to the CGI executable in the PATH_INFO environment
variable.